i wouldnt say avoid it, it would be a lot of money, maybe more than a new blazer but thats a really cool project and if you have sentimental value in your truck its definatly work it and will add to your value.
its expensive and a lot of work but i say go for it if your up to it...
but if you go to a junk yard and find an s10 blazer, grab the axle, driveshafts, tranny, tcase, and anythign else different you see on the 4wd model and do it. i cant really see it being anymore than 1000-1500 dollars at a junk yard... maybe even less?
junkyards should be called discount yards
the only thing is you will run into problems, all projects do, and it may end up less reliable.... its a tough call